1. Field of the Invention
This invention relates to a stent for maintaining the patency of a body passage. In addition to maintaining patency, the stent can serve as drug delivery vehicle to effect localized pharmacologic therapy. The invention has particular application in the field of coronary angioplasty and will be described with reference thereto. In that realization the invention primarily relates to bioabsorbable (and thus biodegradable) stents for placement within a blood vessel, such as a coronary artery, to treat acute arterial closure and to prevent restenosis following angioplasty. However, the invention may also advantageously find application in dilating and maintaining the patency of other body passages, such as the ureters and the fallopian tubes.
2. Description of the Related Art
Coronary angioplasty typically involves the use of a catheter system including a dilation catheter which is introduced via the femoral artery under local anesthesia and is advanced to the site of a stenotic lesion in a coronary artery. The dilation catheter is for example a balloon catheter which is inflated with a fluid once it has been disposed within the targeted stenotic portion of the coronary artery. As the balloon is inflated, the atherosclerotic material along the vessel walls is compressed to thereby dilate the flow passage through the coronary artery.
While balloon angioplasty has become a relatively common and successful procedure, restenosis following angioplasty frequently occurs. Furthermore, the atherosclerotic plaque can crack during expansion which greatly increases the likelihood that the coronary artery will subsequently collapse.
It would therefore be desirable to avoid or minimize restenosis of a blood vessel, such as a coronary artery, by maintaining atherosclerotic plaque in its compressed disposition while at the same time preventing vessel collapse.
With the foregoing object, metallic stents have been developed and carried to stenotic portions of coronary arteries for placement after the vessel segment has been dilated by a balloon catheter or at the time of atherosclerotic plaque compression.
One such metallic stent has been proposed and tested in Europe and described in the article of Sigwart, et al titled "Intravascular Stent to Prevent Occlusion and Restenosis after Transluminal Angioplasty", published in the New England Journal of Medicine, Vol. 316, 12, Mar. 19, 1987, pp. 701-706. That stent is a metallic "Chinese finger handcuff" which can be expanded in diameter while simultaneously reduced in length and compressed in diameter while simultaneously elongated. The stent remains in its distorted configuration after the distorting force is removed.
The metallic stent is made by cutting a desired length from an elongated tube of metal mesh. As a result, it has the disadvantage that metal prongs from the length cutting process remain at the longitudinal ends of the stent. The inherent rigidity of the metal used to form the stent together with the terminal prongs make navigation of the blood vessels to the locus of the targeted stenotic lesion difficult as well as risky from the stand point of injury to healthy tissue along the passage to the target vessel. Further, once the stent has been permanently disposed within the target vessel, the beating of the patient's heart can cause the terminal prongs to damage the healthy vessel walls adjacent to the stenotic portion of the artery, even after endothelial encapsulation. This damage can lead to arterial rupture or aneurysm formation. Finally, because the metallic stent is intended to be chronically implanted within the vessel, continued exposure of the stent to blood can lead to undesirable thrombus formation within the blood vessel.